The present invention relates to an attachment to be attached to a fuel tank made of a synthetic resin.
A fuel tank made by blow molding of a synthetic resin is easily made to have rustproof and lightweight, and also can achieve the high productivity. Therefore, in recent years, such a fuel tank by blow molding of the synthetic resin has been increasingly used as a fuel tank for an automobile as disclosed in Japanese Patent Publication (KOKAI) No. 11-78549, for example.
On the other hand, the fuel tank is attached with various types of attachments, such as a vent valve for leading fuel gas in a space above a liquid surface to an outside of the tank to thereby maintain an internal pressure of the tank constant, a backflow prevention valve which is connected to a filler tube, a fuel pump, and the like. In case the tank is formed of the synthetic resin material, it is preferable that the attachments and the tank can be coupled by thermal welding in view of simplifying the manufacturing process.
However, high-density polyethylene (hereinafter referred to as HDPE), which can be thermally welded, is relatively poor in a property of preventing permeation (hereinafter referred to as a barrier property) of hydrocarbon (hereinafter referred to as HC). Thus, from the viewpoint of preventing air pollution, HDPE is not suitable to be used for the attachments for the gasoline tank.
In order to prevent the permeation or transmission of HC, it is preferable to use a material having a high barrier property, such as ethylene-vinylalcohol copolymer (hereinafter referred to as EVOH). This kind of so-called gasoline barrier material is, however, low in bonding ability by a thermal welding. Thus, if the attachments are formed of the gasoline barrier material, it is difficult to satisfy the bonding strength between the tank and the attachments.
In other words, it is desired that the attachment to be attached to the fuel tank made of the synthetic resin is sufficiently high in strength and rigidity, and is excellent in a property of resisting the swelling against the gasoline, as well as high in a barrier property. However, in order to secure the thermal welding property, that is, the property capable of being welded to the tank in addition to these properties, it is practically impossible to form the attachment by the single material.
Therefore, as in the filler tube connection section and the backflow prevention valve disclosed in Japanese Patent Publication (KOKAI) No. 11-78549, it can be considered to adopt the structure for assembling a plurality of parts, in which materials with optimum properties are respectively used in accordance with positions thereof. However, since each material has the advantage and disadvantage as described above, the aforementioned need can not be achieved by merely forming the filler tube connection section and the backflow prevention valve by the separate members.
The present invention has been made to solve the aforementioned problems in the prior art, and an object of the invention is to provide an attachment to be attached to a fuel tank made of a synthetic resin, in which the strength, rigidity, property of resisting the swelling against gasoline, high barrier property and thermal welding property with respect to the tank can coexist at the high level, respectively.
Further objects and advantages of the invention will be apparent from the following description of the invention.
To achieve the aforementioned object, the first aspect of the present invention provides an attachment to be attached to a fuel tank made of a synthetic resin, which comprises a primary molding portion having a flange and a cylinder or hollow section (valve main body connection section); and an HC barrier material layer (secondary molding portion) formed on at least one part of an inner periphery of the cylinder section. The primary molding portion is formed of a material capable of being welded to the fuel tank. The flange is connected to an outer surface of the fuel tank, and the cylinder section is inserted into the fuel tank.
Also, the cylinder section is provided with a hole for allowing a molten resin material to flow therethrough, and the HC barrier material layer is formed by a two-material molding method. In the attachment to be attached to the fuel tank made of the synthetic resin structured as described above, another part or valve main body is connected to a portion of the material, which is capable of being welded to the fuel tank and is exposed to an outer peripheral surface of the cylinder section.
The attachment to be attached to the fuel tank made of the synthetic resin is formed of the material capable of being welded, and the barrier material by the two-material molding method as described above, so that both the thermal welding property of the portion connected to the fuel tank and the barrier property can coexist. Then, if another part is formed of a material excellent in the property of resisting the swelling against gasoline, and is connected to the portion where the material capable of being welded is exposed, both the strength and the rigidity in a connecting portion to another part can be obtained.
Also, according to the second aspect of the invention, a plurality of holes is formed at portions for substantially equally dividing the circumference of the cylinder section adjacent to the flange. Accordingly, the flow of the secondary resin at the time of the two-material molding can be equalized.
Further, according to the third aspect of the invention, the part includes a cylindrical portion (an enlarged diameter portion) fitted outside the cylinder section. Accordingly, when the portion connected to the fuel tank is expanded together with the fuel tank, the connecting portion of the part tends to be tightly fitted, so that there is no problem that the part is loosened.